Immunosuppressive therapy can produce hematologic improvement in a large proportion of patients with severe aplastic anemia. Antithymocyte globulin (ATG) is the current treatment of choice for patients who do not have histocompatible sibling donors or who are otherwise ineligible for allogeneic bone marrow transplant. About 50% of patients respond to an initial course of ATG, and many nonresponders can be salvaged by subsequent treatment with cyclosporin A (CsA). To determine whether simultaneous administration of these agents can further improve response rates, we are actively enrolling patients in a therapeutic trial of four days of ATG and six months of CsA. We have enrolled 72 patients, with a maximum follow-up of approximately 5 years. The results of the first 55 patients were published as: Rosenfeld SJ, Kimball J, Vining D, Young NS. Superior results of combination immunosuppressive therapy with antithymocyte globulin and cyclosporin A in the treatment of severe aplastic anemia. Blood 1995; 85:3058-3065.